Method and apparatus for the preparation of a medical solution

ABSTRACT

A method and an apparatus for preparation of a medical solution from water and a plurality of concentrates, including at least one acid in gaseous form, comprises the steps of transporting the water from a source through a main conduit and successively adding the plurality of concentrates to the water in the main conduit at a plurality of predetermined points positioned along the main conduit. The apparatus for preparing the medical solution includes a source for supplying the gaseous acid and other concentrates to the plurality of predetermined points along the main conduit, wherein the plurality of predetermined points includes a gas inlet for injecting the acid in gaseous form supplied from the gas source into the main conduit.

This is a division of application Ser. No. 08/132,765 filed on Oct. 6, 1993, which is a continuation of application Ser. No. 07/776,561 filed on Oct. 15, 1991 both now abandoned.

This invention relates generally to a method and apparatus for the preparation of a medical solution. More particularly, this invention relates to a method and apparatus for preparing a dialysis solution from a liquid such as water and a plurality of concentrates, including an acid in gaseous form, whereby respective concentrates are supplied successively to a number of predetermined points along a main conduit which leads from a water source to a dialyzer. Still more particularly, the present invention relates to a method and a system for preparing a dialysis solution from water and a plurality of concentrates including an acid in gaseous form and bicarbonate as a buffer.

BACKGROUND OF THE INVENTION

Methods for the preparation of dialysis solutions using bicarbonate as the buffer are generally disclosed in the prior art. This is shown, for example, in European Patent B1-0 022 922. Likewise, a system for the preparation of a medical solution, preferably intended for dialysis, is also known in the art and is disclosed in U.S. Pat. No. 4,784,495.

In U.S. Pat. No. 4,784,495, a system for preparing a medical solution from water and at least one concentrate in powder form is disclosed. The system disclosed therein includes a water source, a powder source, and at least one liquid concentrate source.

In European Patent B1-0 022 922 a method for the preparation of a medical solution is disclosed in which two liquid concentrates are used. U.S. Pat. No. '495 teaches a substantial improvement over the European Patent '922 by disclosing a system which replaces one of the liquid concentrates with a concentrate in powder form, thereby removing some of the disadvantages associated with the use of concentrates in liquid form. However, a certain quantity of liquid concentrate must still be used in the system disclosed in U.S. Pat. No. '495, which results in various disadvantages.

The present invention discloses an improved method and system for preparation of a medical solution from water and a plurality of concentrates, wherein at least one concentrate is an acid in gaseous form. The use of the gaseous acid as one of the required concentrates makes it possible to use concentrates in powder form for the remaining required concentrates if desired. The only liquid which is absolutely required is water.

Thus, the present invention improves upon the prior art by eliminating problems associated with transporting large quantities of liquid over long distances and reducing the bacteria growth, which is normally considerably less in a powder form concentrate than in a concentrate in liquid form.

SUMMARY OF THE INVENTION

The present invention relates to a method of preparing a dialysis solution which comprises the steps of transporting water through a main conduit while successively adding a plurality of concentrates, including at least one acid in gaseous form, to the water at a plurality of predetermined points along the main conduit.

The present invention also pertains to an apparatus for preparing a dialysis solution from water and a plurality of concentrates wherein at least one of the plurality of concentrates is an acid in gaseous form, the apparatus comprising a water source, a main conduit for transporting the water through the apparatus, and a plurality of concentrate sources for supplying the plurality of concentrates to the water in the main conduit at a plurality of predetermined points, including at least one gas inlet, along the main conduit.

Preferably the invention is intended to be used in connection with a method applied to a dialysis system which uses sodium bicarbonate as the buffer and to which calcium is also supplied. In such a case, the addition of the acid in gas form ought to occur before these substances are blended. In this way the risk of precipitation of solid calcium carbonate is reduced.

Surplus gas which is supplied, if any, can be removed in connection with normal degassing. Thereafter this can possibly be recirculated. This can be desirable, partially from an economic point of view and partially for facilitating the control of the finally supplied quantity of gas.

The control of the supplied quantity of gas can also be facilitated by measuring the pH-value of the prepared solution after the addition of gas and using this for its regulation.

Considerable advantages, such as from a transportation point of view, are gained if the gas is prepared in situ. If this concerns a dialysis system which uses sodium bicarbonate as the buffer, then it is suitable that CO₂ is chosen as such a gas. This can be prepared in situ by mixing a carbonate, preferably sodium bicarbonate, with acid and water. A suitable acid for the preparation is citric acid.

Alternative, CO₂ can be prepared in situ by heating a carbonate, preferably sodium bicarbonate, to a suitable temperature, such as above 50° C. From a hygienic view point, it can be appropriate that water formed during the preparation is separated off before the supply to the main line.

The invention thus relates also to a system for continuous preparation of a medical solution, for example a dialysis solution from water and a plurality of concentrates, including an acid, whereby respective concentrates are arranged to be supplied successively to a number of predetermined points along a main conduit which leads from a water source to a point of consumption, such as a dialyzer. The system is characterized in that one of said dosage points constitutes a gas inlet for the intake of said acid in gas form.

The invention is preferably intended to be applied to a system adapted for use for dialysis with sodium bicarbonate as the buffer and to which calcium is also supplied. In such a case, the predetermined inlet point for the acid in gas form should be positioned between the dosage points for these substances.

The system preferably includes means for measuring the pH-value after the addition of gas. Other measuring devices can however also be used, such as a conductivity meter.

Considerable advantages are attained if the system includes means for preparation of the acid in gas form in situ, such as a device for preparation of CO₂. Other gases can however also be used, such as hydrochloric acid in gas form.

Accordingly, it is an object of the present invention to provide an improved method of preparing a dialysis solution from water and a plurality of concentrates, including an acid, where the acid is supplied in gaseous form.

It is another object of the present invention to provide an improved method for preparing a dialysis solution where at least one of the plurality of concentrates is in powder form.

It is another object of the present invention to provide an improved method for preparing a dialysis solution in which liquid concentrates can be totally avoided.

It is still another method of the present invention to provide an improved method for preparing a dialysis solution where the gaseous acid is prepared in situ.

It is still another object of the present invention to provide an improved method for preparing a dialysis solution which will eliminate or at least greatly diminish problems inherent in the prior art methods such as complications associated with transporting large quantities of liquid over long distances and the problem of bacteria growth in liquid concentrates.

It is still another object of the present invention to provide an improved method for preparing a dialysis solution in which a concentrate can be supplied in the form of a pure acid to eliminate the need of adding metal salts in conjunction with the acid, as prior art methods require.

It is still another object of the present invention to provide an improved apparatus for preparing a dialysis solution from water and a plurality of concentrates in which an acid in gaseous form can be prepared or supplied and transported to a main conduit to become part of the dialysis solution.

These and other objects of the present invention will be more clearly understood when read in conjunction with the detailed description and the accompanying drawings which follow.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a system or a plant for preparation of a medical solution, preferably a dialysis solution in accordance with a preferred form of the present invention.

DETAILED DESCRIPTION

Referring to the drawings, FIG. 1 shows a preferred form of the apparatus for preparation of a medical solution in accordance with the present invention.

In the preferred embodiment shown, water is supplied from a source 1, for example a reverse-osmosis unit. Alternatively, the source 1 can constitute a hospital's central system in which water has already been supplied with one or more concentrates in fixed concentrations. In the following, the expression water source is meant not solely a source for pure water, but also sources for water to which one or more substances have been added. The water is fed via a main conduit 2 with a valve 3 to a heating vessel 4, where it is heated to a temperature, for example circa 37° C. The main conduit 2 then continues via a filter 5 to a mixing point A. A liquid-based concentrate is supplied from a reservoir 34 via a conduit 6 with a filter 7. Alternatively, this concentrate can be supplied in powder form and dissolved in situ by water from the water source 1 being fed therethrough, as is described, for example, in the above-mentioned U.S. Pat. No. 4,784,495 or in the Swedish Patent Application 90.00586-9. The concentrate from the source 34 or concentrate prepared in the above-mentioned way is supplied to the main conduit 2 with the aid of a pump 8.

In order to achieve good mixing, the water and concentrate are fed to a mixing vessel 9 and from there to a conductivity meter 11. So that the mixing vessel 9 can be emptied after treatment has been carried out, it is provided with a separate drainage conduit 12 at its base. The conductivity meter 11 is appropriately arranged to control the pump 8 in order to achieve the correct mixing ratio between water and concentrate.

According to the invention, a concentrate is supplied to the main conduit 2 in the form of a gaseous acid. This acid is drawn from a reservoir 13 therefor. This reservoir can either consist of a gas bottle with suitable gas, for example carbon dioxide or HCl in gas form. Alternatively, it can consist of a device for preparing the gas in situ. By way of example, CO₂ can be prepared in situ by means of a carbonate, preferably sodium bicarbonate, being mixed with acid and water. An example of a suitable acid for this purpose is citric acid. Alternatively, CO₂ can be prepared by warming a carbonate, preferably sodium bicarbonate, to a suitable temperature, such as over 50° C.

The gas from the reservoir 13 is then led through a conduit 14, a valve 15, a flow regulation valve 16 and a non-return valve 17 to a mixing point B in the main conduit 2.

A third concentrate from a reservoir 20 in the form of a powder cartridge is then supplied to a point C in the main conduit with the aid of a pump 18 via conduit 19. The powder therein is dissolved continuously by water being drawn from the heating vessel via a tube 21 and a conduit 22 with a filter 23. The conduit 19 also includes a filter 24. The dissolving of the powder in the cartridge 20 can occur in a way as described in the above-mentioned U.S. Pat. No. '495.

The prepared liquid is delivered from the mixing point C via a throttle 25 and bubble chamber 26 with the aid of a pump 27 to a bubble trap 28. Through this arrangement, bubbles are formed from mainly air dissolved in the liquid and any surplus gas supplied from the reservoir 13. These bubbles are enlarged in the bubble chamber 26 and removed in the bubble trap 28 in a not shown way. These together with a smaller quantity of liquid, can possibly be led directly to a drain or may also be recirculated so that surplus gas can also be dissolved. Like the mixing vessel 9, the bubble chamber 26 is also provided with a drainage conduit 29 at its base. Thus, this can be completely emptied when the system for example is to be cleaned.

The main conduit 2 extends from the bubble trap 28 via a pH-meter 30, a conductivity meter 31, a throttle 32 and a pump 33 to a not shown dialyzer. The pH-meter 30 is hereby suitably arranged to control the flow regulator 16 in the conduit 14. The conductivity meter 31 is further suitably arranged to control the pump 18 in the conduit 19. These pumps can alternatively consist of some type of adjustable dosage pump to which a suitable value can be inputted in relation to the flow of liquid through the main conduit 2.

The components 32 and 33 can be parts of a constant flow device of the type which is described in more detail in U.S. Pat. No. 4,762,618. In such a case, a pressure meter is provided therebetween which controls the pump 33 so that a constant pressure drop is maintained across the throttle 32 and thereby a constant flow to the dialyzer.

EXAMPLE FOR PREPARATION OF CO₂

1. Sodium bicarbonate mixed with acid and water

Acid in dry form, such as citric acid, is mixed in suitable quantities with sodium bicarbonate. For dialysis treatment the suitable quantities are circa 37 g citric acid and 45 g sodium bicarbonate. When water is added, the formation of CO₂ commences. In order to moderate the supply of gas, either the water supply to the powder mixture can be regulated and thereby control the gas production, or the gas can be allowed to be collected in a reservoir under pressure and the supply of gas to the main conduit can be regulated with a flow regulating device.

2. Sodium bicarbonate heated to conversion temperature

Dry sodium bicarbonate is heated to a temperature above 50° C. in a gas-tight vessel which is connected to the point of consumption. The gas production is directly proportional to this supply of energy. In this way, the gas production can be controlled as needed. In order to control the quantity of supplied energy, either the gas flow or the pH-value in the ready dialysis liquid can be measured.

DETAIL INFORMATION

Surplus gas can either be separated off in connection with the normal degassifying or can be brought to recirculate in the system.

Parameters which effect the quantity of supplied acid are, amongst others, the pressure at the dosage intake point, the temperature of the liquid, exposure time for the gas (contact distance/flow velocity) and contact surface (total bubble surface).

Other gases such as hydrochloric acid in gas form can be used in the preparation of the dialysis solution. The hydrochloric acid need not be in gas form from the outset. Instead this can be generated in situ by mixing for example sodium chloride with suitable acid, such as sulfuric acid, during heating. However, it is preferable to use CO₂. Furthermore, it should be noted that the conductivity meter 31 can be arranged solely for control of the preparation. In such case, the flow control valve 16 can totally control the gas flow in the conduit 14. Besides regulating means, in such a case this can also include means for measuring the flow. Furthermore, the parts included in the described system can be carried within wide limits concerning both form and function.

While the foregoing description and figures are directed to the preferred embodiment of the method and system for preparation of a dialysis solution in accordance with the present invention, it should be appreciated that certain modifications can be made, and are, indeed, encouraged to be made, in the materials, structure and arrangement of the disclosed embodiment without departing from the spirit and scope of the present invention which is intended to be captured by the claims set forth below. 

We claim:
 1. Apparatus for continuously preparing a medical dialysis solution from water and a plurality of concentrates contemporaneous with its use wherein one of said concentrates includes a carbonate, another one of said concentrates includes calcium, and one of said concentrates is carbon dioxide gas, the apparatus comprising water supply means for supplying a liquid comprising water to said apparatus, a closed main conduit means for transporting said supply of water through said apparatus to be directly supplied therefrom for said use, first concentrate supply means for supplying a first one of said concentrates to a first predetermined point on said main conduit means, second concentrate supply means for supplying a second one of said concentrates comprising said carbon dioxide gas to a second predetermined point on said main conduit downstream of said first predetermined point, and third concentrate supply means for supplying a third one of said concentrates to a third predetermined point on said main conduit means downstream of said second predetermined point whereby a medical solution including said first, second and third concentrates is continuously provided for said contemporaneous use.
 2. The apparatus as claimed in claim 1 including carbon dioxide gas supply means for supplying said carbon dioxide gas from an outside gas source.
 3. The apparatus as claimed in claim 2 wherein said second concentrate supply means comprises means for preparing said carbon dioxide gas in situ.
 4. An apparatus as claimed in claim 3 wherein said means for preparing said carbon dioxide gas in situ comprises means for heating a carbonate to a temperature above about 50° C.
 5. An apparatus as claimed in claim 4 wherein said carbonate comprises sodium bicarbonate.
 6. An apparatus as claimed in claim 4 wherein said means for preparing said carbon dioxide gas in situ comprises means for mixing a carbonate with an acid in water.
 7. An apparatus as claimed in claim 6 wherein said carbonate comprises sodium carbonate and said acid comprises citric acid.
 8. An apparatus as claimed in claim 1 including means for measuring the pH value of said medical solution at a point downstream of said second predetermined point.
 9. An apparatus as claimed in claim 1 further comprising heating means for heating said water prior to mixing said water with said first, second and third concentrates in said main conduit means.
 10. An apparatus as claimed in claim 9 further including at least one reservoir cartridge for maintaining at least one of said first and third concentrates in powder form and water supply means for supplying said heated water to said reservoir cartridge for dissolving the concentrate contained therein prior to transporting such concentrate into said main conduit.
 11. Apparatus as claimed in claim 1 in further comprising means for removing bubbles of surplus gas from said dialysis solution and recirculating said surplus gas into the apparatus.
 12. Apparatus as claimed in claim 11 wherein said second concentrate supply means includes means for contolling the amount of carbon dioxide gas supplied by said second concentrate supply means. 